1. Field of the Invention
The invention relates to a thin film magnetic head having at least an inductive-type magnetic transducer for writing and a method of manufacturing the same.
2. Description of the Related Art
Performance improvement in thin film magnetic heads has been sought in accordance with an increase in surface recording density of a hard disk device. A composite thin film magnetic head, which is made of a layered structure including a recording head with an inductive-type magnetic transducer for writing and a reproducing head with a magnetoresistive (MR) element for reading, is widely used as a thin film magnetic head. As MR elements there are an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called an AMR head or simply an MR head. A reproducing head using the GMR element is called a GMR head. The AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. The GMR head is used as a reproducing head whose surface recording density is more than 3 gigabit per square inch.
The AMAR head includes an AMR film having an AMR effect. In a GMR head the AMR film is replaced with a GMR film having the GMR effect and the configuration of the GMR head is similar to that of the AMR head. However, the GMR film exhibits a greater change in resistance under a specific external magnetic field compared to the AMR film. Therefore, the reproducing output of the GMR head becomes about three to five times greater than that of the AMR head.
An MR film may be changed in order to improve the performance of a reproducing head. In general, an AMR film is a film made of a magnetic substance which exhibits the MR effect and has a single-layered structure. In contrast, many of the GMR films have a multi-layered structure consisting a plurality of films. There are several types of mechanisms which produce the GMR effect. The layer structure of the GMR film depends on those mechanisms. GMR films include a superlattice GMR film, a granular film, a spin valve film and so on. The spin valve film is most sufficient since the film has a relatively simple structure, exhibits a great change in resistance in a low magnetic field, and is suitable for mass production. The performance of a reproducing head is thus easily improved by changing an AMR film with a GMR film and the like with an excellent magnetoresistive sensitivity.
As a primary factor for determining the performance of a reproducing head, there is a pattern width, especially an MR height. The MR height is the length (height) between the end of an MR element closer to an air bearing surface and the other end. The MR height is originally controlled by an amount of grinding when the air bearing surface is processed. The air bearing surface (ABS) here is a surface of a thin film magnetic head that faces a magnetic recording medium and is also called a track surface.
Performance improvement in a recording head have also been expected in accordance with the performance improvement in a reproducing head. It is required to increase the track density of a magnetic recording medium in order to increase the recording density among the performance of a recording head. In order to achieve this, a recording head with a narrow track structure in which the width of a bottom pole and a top pole sandwiching a write gap on the air bearing surface is required to be reduced to the order of some microns to submicron. Semiconductor process technique is used to achieve the narrow track structure.
Another factor which determines the performance of a recording head is the throat height (TH). The throat height is the length (height) of a portion (magnetic pole portion) which is from the air bearing surface to an edge of an insulating layer which electrically isolates the thin film coil. Reducing the throat height is desired in order to improve the performance of a recording head. The throat height is also controlled by an amount of grinding when the air bearing surface is processed.
In order to improve the performance of a thin film magnetic head, it is important to form the recording head and the reproducing head as described in well balance.
Here, an example of a method of manufacturing a composite thin film magnetic head will be described with reference to FIGS. 16A, 16B to FIGS. 21A, 21B as an example of a method of manufacturing a thin film magnetic head of the related art.
As shown in FIG. 16, an insulating layer 102 made of, for example, alumina (aluminum oxide, Al.sub.2 O.sub.3) is formed to a thickness of about 5 to 10 .mu.m on a substrate 101 made of, for example, aluminum oxide and titanium carbide (Al.sub.2 O.sub.3 TiC). Further, a bottom shield layer 103 for a reproducing head made of, for example, permalloy (NiFe) is formed on the insulating layer 102.
Next, as shown in FIG. 17, for example, alumina of about 100-200 nm in thickness is deposited on the bottom shield layer 103 to form a shield gap film 104. Next, an MR film 105 of tens of nanometers in thickness for making up the MR element for reproducing is formed on the shield gap film 104, and photolithography with high precision is applied to obtain a desired shape. Next, a lead terminal layer 106 for the MR film 105 is formed by lift-off method. Next, a shield gap film 107 is formed on the shield gap film 104, the MR film 105 and the lead terminal layer 106, and the MR film 105 and the lead terminal layer 106 are buried in the shield gap films 104 and 107. Next, a top shield-cum-bottom pole (called bottom pole in the followings) 108 of about 3 .mu.m in thickness made of, for example, permalloy (NiFe), which is a material used for both of the reproducing head and the recording head, is formed on the shield gap film 107.
Next, as shown in FIG. 18, a write gap layer 109 of about 200 nm in thickness made of an insulating layer such as an alumina film is formed on the bottom pole 108. Further, an opening 109a for connecting the top pole and the bottom pole is formed through patterning the write gap layer 109 by photolithography. Next, a pole tip 110 is formed with magnetic materials made of permalloy (NiFe) and nitride ferrous (FeN) through plating method, while a connecting-portion pattern 110a of the top pole and the bottom pole is formed. The bottom pole 108 and a top pole layer 116 which is to be described later are connected by the connecting-portion pattern 110a and so that forming a through hole after CMP (Chemical and Mechanical Polishing) procedure, which is to be described later, becomes easier.
Next, as shown in FIG. 19, the write gap layer 109 and the bottom pole 108 are etched about 0.3-0.5 .mu.m by ion milling with the pole tip 110 being a mask. By etching the bottom pole 108 to be a trim structure, widening of effective write track width can be avoided (that is, suppressing spread of magnetic flux in the bottom pole when data is being written). Next, after an insulating layer 111 of about 3 .mu.m, made of, for example, alumina is formed all over the surface, the whole surface is flattened by CMP.
Next, as shown in FIG. 20 a first layer of thin film coil 112 for an inductive-type recording head made of, for example, copper (Cu) is selectively formed on the insulating layer 111 by, for example, plating method. Further, a photoresist film 113 is formed in a desired pattern on the insulating layer 111 and the thin film coil 112 by photolithography with high precision. Further, a heat treatment of desired temperature is applied to flatten the photoresist film 113 and to insulate between the turns of the thin film coil 112. Likewise, a second layer of thin film coil 114 and a photoresist film 115 are formed on the photoresist film 113, and a heat treatment of desired temperature is applied to flatten the photoresist film 115 and to insulate between the turns of the thin film coils 114.
Next, as shown in FIG. 21, a top yoke-cum-top pole layer (called a top pole layer in the followings) 116 made of, for example, permalloy, which is a magnetic material for recording heads, is formed on the top pole 110, the photoresist films 113 and 115. The top pole layer 116 is in contact with the bottom pole 108 in a position recessed from the thin film coils 112 and 114, while being magnetically coupled to the bottom pole 108. Further, an over coat layer 117 made of, for example, alumina is formed on the top pole layer 116. At last, a track surface (air bearing surface) of the recording head and the reproducing head is formed through performing machine processing on the slider to complete a thin film magnetic head.
In FIG. 21, TH represents the throat height and MR-H represents the MR height. Further, P2W represents the track (magnetic pole) width.
As an factor for determining the performance of a thin film magnetic head, there is an apex angle as represented by .theta. in FIG. 21 besides the throat height TH and the MR height MR-H and so on. The apex angle is an angle between a line connecting the corner of a side surface of the track surface of the photoresist films 113, 115 and an upper surface of the top pole layer 116.
To improve the performance of a thin film magnetic head, it is important to precisely form the throat height TH, the MR height MR-H and the apex angle .theta. as shown in FIG. 21
In the application, problems regarding precise control of a track width P2W will be specifically discussed. That is, precise formation of the track width P2W is required since it determines a track width of a recording head. Especially in these years, submicron measurement of 1.0 .mu.m or less is required in order to make a high surface density recording possible, that is, to form a recording head with a narrow track structure. To achieve this, a technique for processing a top pole to submicron using a semiconductor processing technique, and using magnetic materials having higher saturation flux density are desired.
Here, the problem is that it is difficult to minutely form the top pole layer 116 on a coil portion (apex area) which is protruded like a mountain covered with photoresist films (for example, the photoresist films 113 and 115 shown in FIG. 21).
As a method of forming the top pole, frame plating method is used as, disclosed in, for example, Japanese Patent Application laid-open in Hei 7-262519. When the top pole is formed by the frame plating method, first, a thin electrode film made of, for example, permalloy is formed all over the apex area. Next, a frame is formed by applying photoresist on it, and patterning it through photolithography. Further, the top pole is formed through plating method with the electrode film formed earlier being a seed layer.
By the way, there is, for example, 7-10 .mu.m or more difference in height between the apex area and other areas. If the film thickness of the photoresist formed on the apex area is required to be 3 .mu.m or more, a photoresist film of 8-10 .mu.m or more in thickness is formed in the lower part of the apex area since the photoresist with liquidity gathers into a lower area. To form a narrow track as described, a pattern with submicron width is required to be formed with a photoresist film. Accordingly, forming a micro pattern with submicron width with a photoresist film of 8-10 .mu.m or more in thickness is required, however, it has been extremely difficult.
Further, during an exposure of photolithography, a light for the exposure reflects by an electrode film made of, for example, permalloy, and the photoresist is exposed also by the reflecting light causing deformation of the photoresist pattern. As a result, the top pole can not be formed in a desired shape and so on, which means, its side walls take a shape of being rounded. As described, it has been extremely difficult with the related art to precisely control the track P2W and to precisely form the top pole to have a narrow track structure.
For the reasons described above, as shown in the procedure of an example of the related art in FIG. 18 to FIG. 21, a method of connecting the pole tip 110 and a yoke area-cum-top pole layer 116 after forming a track width of 1.0 .mu.m or less with the pole tip 110 which is effective for forming a narrow track of a recording head, that is, a method of dividing the regular top pole into the pole tip 110 for determining the track width and the top pole layer 116 which becomes the yoke for inducing magnetic flux is employed (Ref Japanese Patent Application laid-open Sho 62-245509, Sho 60-10409). By dividing the top pole into two as described, the pole tip 110 can be minutely processed to submicron width on a flat surface of the write gap layer 109. The track width of the recording head is determined by the pole tip 110 so that the other top pole layer 116 is not required to be minutely processed comparing to the pole tip 110.
However, when the track width of the recording head becomes extremely fine, especially 0.5 .mu.m or less, a process precision with submicron width is required in the top pole layer 116. That is, if the measurement difference in a lateral direction of the pole tip 110 and the top pole layer 116 is too significant when looking at them from the track surface 118 side, as described above, a side write occurs and a problem that writing is performed in a region other than the originally designated data recording region in a hard disk occurs. As a result, the effective track width becomes wider and a problem that writing is performed in a region other than the originally designated data recording region in a hard disk occurs.
As a result, not only the pole tip 110 but also the top pole layer 116 is required to be processed to the submicron width, however, it is difficult to perform fine-process of the top pole layer 116 since there is a significant difference in heights as described above in the apex area under the top pole layer 116.
The invention is designed to overcome the foregoing problems. It is an object to provide a thin film magnetic head in which not only the pole tip but also the top pole layer can be minutely processed to submicron width while the performance of the recording head is especially improved, and a method of manufacturing the same.